function addBox(){
    $(document.createElement("div"))
        .attr("id","mengban")
        .css({
            position : "fixed",
            "z-index" : 280,
            left : "0px",
            top : 0,
            zoom : 1,
            width : $(window).width(),
            height : $(window).height(),
            "overflow":"hidden"
        }).appendTo($(document.body))
        .append("<div  id='_alpha' style='position:absolute;z-index:2;width:100%;height:100%;left:0;top:0;opacity:0.3;filter:Alpha(opacity=30);background:#000'></div><div id='_iframe' style='position:absolute;z-index:5;top:40%;left:50%;'></div>");

    var src='/Public/img/loading.gif';

    $("#_iframe").append("<img src='"+src+"' style='width:50px;margin-left:-25px;'/>");
}